Redated Fossil Upsets Map of Man's Evolution

New evidence strongly suggests that the human race migrated from its African cradle to Asia nearly one million years earlier than most scientists believed. The discovery will force anthropologists to re-examine some long-held beliefs about how and where evolutionary turning points made mankind master of the world.

In a paper presented yesterday at a meeting of the American Association for the Advancement of Science in San Francisco, Dr. Carl C. Swisher 3d of the Institute of Human Origins in Berkeley, Calif., reported that skull fragments of Homo erectus found some time ago on the Indonesian island of Java are up to 1.8 million years old -- as old as the oldest Homo erectus fossils ever found in Africa.

This may mean, he said in an interview, that the early human beings commonly lumped together under the species name Homo erectus may have belonged to two or more separate species that evolved independently from a common ancestor.

Details of the evolutionary pathways that led from the earliest hominids of Africa to modern Homo sapiens sapiens have been enigmas and the source of controversy. Although most anthropologists believe that the human race originated in Africa, the new measurements open the possibility that although man's prehuman ancestors began in Africa, different variants of the primate genus Homo may have independently evolved in Africa, Europe and Asia.

Homo erectus is the name commonly given to a group of primates many anthropologists believe to be the first entitled to be called human beings. From Homo erectus evolved Homo sapiens and its present-day subspecies, Homo sapiens sapiens. Somewhere along the way, either as an intermediate or an offshoot of the evolutionary line, Neanderthals arose, flourished and died out about 35,000 years ago.

But none of the evolutionary connections among human ancestors are clear.

"This is certainly going to prompt a lot of discussion and theorizing," Dr. Swisher said. "But the disagreements will have to do with interpretation, not the methods by which we determined the new dates. They are well established."

Dr. Swisher and his American and Indonesian colleagues, specialists in measuring the ages of rocks, used a new method to date the Indonesian fossils.

The skull fragments came from two sites in central Java. The first, the skull cap of a child, named the Mojokerto child, was found in 1936 near the village of Perning. Two other sets of skull fragments, called Meganthropus, were found near Sangiran in the late 1970's. Anthropologists tentatively assigned all three fossils to the species Homo erectus, previously known as Pithecanthropus erectus.

Previous rough estimates of the ages of the fossils were mainly based on the geology of the rocks in which they were found. This included the presence or absence of fossil species that lived in certain periods of geological history.

Until now, the oldest human remains in Asia were believed to be about one million years old. By comparison, the oldest human remains in Africa were estimated at 1.8 million years. Many anthropologists believed that the age difference between the earliest African and earliest Asian Homo erectus fossils implied that the species got its start in Africa and then radiated much later to other continents. Troublesome Theory

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For example, Homo erectus in Africa devised specialized, two-faced stone cleavers and hand axes, collectively known as the Acheulean tool kit, that are frequently found at Homo erectus sites in Africa but not in Asia. If Homo erectus developed in Africa, invented these useful tools and then set out to colonize Asia, why did he not take his tools along? If, on the other hand, separate branches of the Homo erectus tree evolved simultaneously in Africa and Asia, as the new fossil dates seem to suggest, this problem would be explained: the founders of the Asian branch left home before their African cousins had had time to invent Acheulean tools.

The new date of the Mojokerto child, Dr. Swisher's group has determined, is about 1.81 million years, and the Sangiran fossils are about 1.66 million years old. The oldest African Homo erectus fossils, found at Koobi Fora in Kenya, has been dated at about the same age as the Mojokerto child.

Dr. Swisher and his colleagues did not analyze the fossils themselves but determined the ages of the pumice and other volcanic rock in which the fossils were embedded when they were excavated. They used an extremely sensitive argon-argon method, by which they measured the ratio of stable argon gas to a slightly radioactive, unstable form of argon in the rock. Because of the gradual radioactive decay of elements in the rock, the ratio of argon isotopes, or forms, changes very slowly with time, and the degrees of change can be interpreted as ages. The method, Dr. Swisher says, yields dates accurate to within about 70,000 years, a small margin of error considering the great age of the rock.

The journal Science, which will publish the report on the Java fossils tomorrow, is also publishing comments from other scientists on the achievement. Dr. Francis Brown, a geologist at the University of Utah, said that he was sure the date of the rock was accurate but that there was always a possibility that old rock could have been mixed with younger rock embedding the fossils, yielding a false age.

Dr. Garniss Curtis, a member of the research group and Dr. Swisher's former professor, said he had believed for nearly three decades that the Java fossils were much older than most scientists at the time believed. In the 1960's, Dr. Curtis applied a dating method called potassium-argon (based on the slow radioactive decay of an isotope of potassium to argon) to rock that had contained the child's skull cap and had found an age of 1.9 million years. But because the method was much less accurate than the new argon-argon method, his result was generally dismissed.

Science also quoted Dr. Curtis as saying, "anthropologists didn't want to see anything that old from Java," because it would conflict with the theory that Homo erectus radiated from Africa nearly one million years after the species appeared.

Since the first fossil hominid was discovered in Java in 1891, a profusion of scientific names has been assigned to various human remains that may or may not all belong to the species Homo erectus. The first Java fossil was initially named Anthropopithecus erectus, or upright man-ape, and then renamed Pithecanthropus erectus, or upright ape-man. Similar human remains found in Java have been given such names as Pithecanthropus dubius, Pithecanthropus robustus, Meganthropus, which was renamed Australopithecus palaeojavanicus and Homo erectus ngandongensis (soloensis).

Fossils found in China of a species once popularly known as Peking Man are also believed to have represented the Homo erectus line, as do some fossils found in Europe. The Peking bones disappeared in World War II.

Asked whether it would be possible to date the soil from which the Chinese Homo erectus fossils were taken, Dr. Swisher said it was doubtful. The argon-argon method requires volcanic rock, he said, and the sites where Homo erectus has been found in China do not contain volcanic rock.

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A version of this article appears in print on February 24, 1994, on Page A00001 of the National edition with the headline: Redated Fossil Upsets Map of Man's Evolution. Order Reprints|Today's Paper|Subscribe